Preparation of paper pulps from dicotyledonous plants

Abstract

Paper pulp is prepared from dicotyledonous plants by stirring said plants in an alkaline solution in the presence of a surfactant and stain inhibiting agent to obtain a stock containing a woody core fraction and a bark fraction containing bast fibers, separating said fractions and then cooking and bleaching the bark fraction in an alkaline solution containing an oxidizing agent and an alkyl sulfate surfactant.

What I claim is: 
     
       1. A process for the preparation of pulps for paper from dicotyledonous plants, comprising the steps of: stirring in a pulper, the dicotyledonous plants in an alkaline solution in the presence of a surfactant and at least one stain inhibiting agent selected from the group consisting of peroxides and sodium hypochlorite, which agent prevents staining of the plant fibers in alkaline media by blocking the chromophoric groups of the dicotyledonous plants, in order to obtain a stock containing a both woody core fraction and a bark fraction containing bast fibers;   dividing said stock into a woody core fraction and a bark fiber fraction; and then   subsequently cooking and bleaching said bark fraction under atmospheric pressure in an alkaline solution containing an alkyl sulfate surfactant and an oxidizing agent selected from the group consisting of hydrogen peroxide and tertiary butyl hydroperoxide.   
     
     
       2. A process according to claim 1, wherein before cooking and bleaching, the bark fraction is treated with active chlorine generating agents. 
     
     
       3. A process according to claim 2, wherein the treatment with the active chlorine generating agents is performed with 2-10% active chlorine at a temperature between room temperature and 80° C for 30-120 minutes. 
     
     
       4. A process according to claim 1, wherein the temperature of the alkaline solution is about 75° C. 
     
     
       5. A process according to claim 1, wherein the alkaline solution employed in said stirring step is obtained by dissolving in water an alkaline agent selected from the group consisting of sodium hydroxide, sodium sulfite and a mixture thereof. 
     
     
       6. A process according to claim 1, wherein the cooking and bleaching of the bark fraction is carried out at 50°-90° C for 30-120 minutes with 2-6% peroxide calculated as H 2  O 2 , 5-20% of alkali and 0.1-0.5% of alkyl sulfate surfactant, all percentages being based on the weight of dry raw material. 
     
     
       7. A process according to claim 1, wherein after the cooking and bleaching step the prepared pulp is washed and acidified to a pH of 5-6 with an aqueous solution of a member selected from the group consisting of sulphur dioxide and oxalic acid.